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/*! @file vlc.h
*
* @brief Declaration of the data structures for variable-length decoding
*
* @version 1.0.0
*
* (C) Copyright 2018 GoPro Inc (http://gopro.com/).
*
* Licensed under either:
* - Apache License, Version 2.0, http://www.apache.org/licenses/LICENSE-2.0
* - MIT license, http://opensource.org/licenses/MIT
* at your option.
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef VLC_H
#define VLC_H
// Codewords for the sign bits that follow a non-zero value
#define VLC_POSITIVE_CODE 0x0 //!< Code that indicates a positive value
#define VLC_NEGATIVE_CODE 0x1 //!< Code that indicates a negative value
#define VLC_SIGNCODE_SIZE 1 //!< Size of the code for sign suffix
/*!
@brief Codebook entries for arbitrary runs and values
The codebook data structure allows runs of an arbitrary value,
but all codec implementations only use runs of zeros. The
codeword for a non-zero value is followed by the sign bit.
@todo Could add the sign bit to the magnitude entries in this
table if it improves performance or makes the code more clear.
*/
typedef struct _rlv {
uint_fast8_t size; //!< Size of code word in bits
uint32_t bits; //!< Code word bits right justified
uint32_t count; //!< Run length
int32_t value; //!< Run value (unsigned)
} RLV;
/*!
@brief Declaration of a codebook
This data structure is often called the master codebook to distinguish
it from the encoding tables that are derived from the codebook. The
codebook has a header that is immediately followed by the codebook entries.
Each entry is an @ref RLV data structure that contains the codeword and
the size of the codeword in bits. Each codeword represent a run length
and value. The current codec implementation only supports runs of zeros,
so the run length is one for non-zero values. A non-zero value is an
unsigned coefficient magnitude. Special codewords that mark significant
locations in the bitstream are indicated by a run length of zero and the
value indicates the type of marker.
The codebook is generated by a separate program that takes as input a table
of the frequencies of coefficient magnitudes and runs of zeros.
*/
typedef struct _codebook
{
uint32_t length; //!< Number of entries in the code book
// The length is followed by the RLV entries
} CODEBOOK;
//! Macro used to define the codebook generated by the Huffman program
#define RLVTABLE(n) \
static struct \
{ \
uint32_t length; \
RLV entries[n]; \
}
/*!
@brief Structure returned by the run length decoding routines
The value returned may be signed if the routine that was called
to parse the bitstream found a run of a non-zero value and then
parsed the sign bit that follows the magnitude.
*/
typedef struct _run {
uint32_t count; //!< Run length count
int32_t value; //!< Run length value
} RUN;
//! Initializer for the run length data structure
#define RUN_INITIALIZER {0, 0}
#ifdef __cplusplus
extern "C" {
#endif
CODEC_ERROR GetRlv(BITSTREAM *stream, CODEBOOK *codebook, RUN *run);
CODEC_ERROR GetRun(BITSTREAM *stream, CODEBOOK *codebook, RUN *run);
#ifdef __cplusplus
}
#endif
#endif // VLC_H
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